Silicon-on-insulators (SOIs) are characterized in structure in employing a buried oxide layer between an active layer (or referred to as a device layer, i.e., a silicon layer from which integrated circuit devices are formed) and a substrate to isolate electrical connection between the active layer and the substrate. Primary difference in structure between an SOI circuit and a bulk silicon circuit lies in that, all silicon-based devices of the bulk silicon circuit are formed in an epitaxial layer and the devices are electrically connected to a substrate underlying the epitaxial layer, with reversely biased PN junctions isolating high-voltage and low-voltage portions of the circuit and isolating the active layer and the substrate, whilst in the SOI circuit, an insulator layer (i.e., the buried oxide layer) is employed to accomplish the complete isolation between high-voltage and low-voltage portions of the circuit and between the active layer and the substrate to achieve thorough elimination of electrical connection. Such structural characteristics provide the SOI circuit with a number of advantages, such as reduction in parasitic effect and power consumption and improvement in speed, integration density and noise immunity.
However, the conventional SOI RF devices (i.e., RF devices formed on SOIs) have been found suffering from a problem that the amplification of an RF signal can alter certain electrical characteristics of the substrate and the alteration will in turn cause distortion in the RF signal. We have invented an SOI RF device and a method of forming such an SOI RF device, capable of suppress the drawbacks of the conventional SOI RF devices.